Vehicle brake slack adjusters for heavy duty vehicles requiring high braking power have either a manual adjustment of the device to compensate for brake lining wear or an automatic adjustment. Brake lining wear causes a gradual increase in the brake cylinder piston stroke with a resulting decrease in braking efficiency between manual adjustments. In view of the problems attendent with manual adjustment, automatic slack adjusters have been developed to provide substantially automatic and continuous compensation for the wear of the brake linings.
Automatically adjusting brake levers employing brake chamber piston rod linkages utilize the relative motion between the lever and the piston rod to actuate the adjusting mechanism on each piston stroke. Many of the presently known automatic slack adjusters, as exemplified by U.S. Pat. Nos. 3,351,164 and 3,392,810 provide a ground or stationary reference point on the vehicle which cooperates with a driving member in the rotatable braking lever to provide movement of the driving member upon excessive rotation of the braking lever beyond a predetermined position; the movement of the driving member acting to cause rotation of a worm on a load biased rotatable wormshaft and clutch. The worm meshes with a worm gear on the braking cam shaft to adjust the amount of slack in the system.
The ground or stationary reference point is often achieved by a control arm on the braking lever which must be secured to the vehicle axle or brake plate by means of an anchor bracket. It is difficult at times to devise a simple bracket to do the job since the environment for each pair of slack adjusters for a tractor-trailer combination may be different for each axle and right-hand and left-hand units are needed. This results in tooling up and stocking a multiplicity of brackets adding considerably to the cost and complicating field servicing.